The absolute value of thermoelectric power of a metal material such as lead, platinum, etc., is a physical property value which is indispensable for a relative measurement method of thermoelectric power that is widely used in the field of physical property measurement. Absolute thermoelectric power is derived by comparative measurement with a superconductor as a reference material, using the fact that the Seebeck coefficient is zero in the superconducting state. This method causes a measurable temperature region to be restricted to a temperature which is lower than the superconducting transition temperature, so that it is necessary to derive the absolute thermoelectric power using the Kelvin relation from the measurable Thomson coefficient to expand the temperature measurement region.
Here, thermoelectric power S is generally defined as S=ΔV/ΔT using a voltage ΔV which is produced when a temperature difference ΔT is imparted to a metal or a semiconductor. A measurement value of the thermoelectric power based on this definition more accurately applies to a relative value, or, in other words, a difference in the thermoelectric power of a metal to be measured and a wiring material (metal), so that a correction which takes into account the thermoelectric power of the wiring material is needed to determine the absolute thermoelectric power of the metal to be measured. More specifically, when the thermoelectric power of the metal to be measured is around several tens of μ V/K, an effect of such a correction cannot be neglected.
Now, while a number of devices for measuring the thermoelectric power have already been commercially available, a simple and convenient relative measurement method is adopted as the measurement principle in any one of the devices. Here, while, with the relative measurement method, it is necessary to correct a value of the thermoelectric power of the metal to be measured by measuring the absolute thermoelectric power of the wiring material included in the device, there are currently no facilities for actually measuring the absolute thermoelectric power, so that, as shown in NON-PATENT DOCUMENTS 2-4, in reality, each manufacturer depends on data on measurements of the absolute thermoelectric power that were carried out between the 1970's and the 1980's.
More specifically, ever since Nettleton proposed, in 1916, a method of calculating the Thomson coefficient when a polarity-inverted DC voltage is applied to a thin metal wire (below called “a DC inversion method”) (see NON-PATENT DOCUMENT 1), the absolute thermoelectric power has been measured on lead, copper, platinum, etc., and determined for 0 to 1600 Kelvin (K) by Robert et al., (see NON-PATENT DOCUMENTS 2-4). Then, these measurement results have been widely adopted as reference values up to the present.
Here, the above-described Thomson coefficient μ is shown with the following Equation (1):
                    μ        =                                            4              ⁢              κ              ⁢                                                          ⁢              a              ⁢                                                          ⁢              δ              ⁢                                                          ⁢              T                        ⁢                                                                                    (                                                T                  2                                -                                  T                  1                                            )                        ⁢                          I              ⁢              L                                                          (        1        )            
In the above Equation, T1 and T2 are temperatures in units of K at both ends of the metal to be measured when a voltage is applied to the both ends; I is a current in units of A, flowing through the metal; L is a length in m from an end to a midpoint of the metal; κ is a thermal conductivity in units of W/mK of the metal; a is a cross-sectional area in units of m2 of the metal; and δT represents a half of a temperature change in units of K at the center (the midpoint) of the metal when a polarity-inverted DC current is passed through the metal to be measured.
Then, the absolute thermoelectric power S is calculated with the Kelvin equation, or Equation (2) below:
                    S        =                              S            ⁡                          (                              T                0                            )                                +                                    ∫                              T                0                            T                        ⁢                                                            μ                  ⁡                                      (                    T                    )                                                  T                            ⁢                                                          ⁢              d              ⁢                                                          ⁢              T                                                          (        2        )            
In the above Equation, T0 means 92K, which is the superconducting transition temperature.
Moreover, from Equation (2), it is seen that the Thomson coefficient μ needs to be correctly determined to accurately determine the absolute thermoelectric power S.
Here, while a related-art absolute thermoelectric power measurement method determines the Thomson coefficient by measuring a temperature change caused by applying a DC voltage to a metal to be measured to which a temperature gradient is provided, a heat generation amount caused by the Thomson effect has a small value of less than or equal to approximately 1/100 of the Joule heat, which is generated at the same time.
Now, to perform accurate measurement of the heat amount, the above-described DC inversion method is being adopted in which the polarity-inverted DC current is passed through a subject to cancel out an effect of the Joule heat, which is generated by the current.
Now, the below-mentioned PATENT DOCUMENT 1 discloses a thermoelectric material evaluation device and a thermoelectric property evaluation method that calculate a thermoelectric power based on the above definition (ΔV/ΔT) of the absolute thermoelectric power S.
Moreover, the Thomson coefficient derivation equation (Nettleton's equation) is derived by the DC method based on the heat conduction equations in the below-mentioned NON-PATENT DOCUMENT 1, while the Nettleton's equation is used to actually measure, for the first time, the Seebeck coefficient from the Thomson coefficient for lead metal in NON-PATENT DOCUMENT 2.
Furthermore, the Seebeck coefficient is actually measured, for the first time, from the Thomson coefficient for copper metal by the current injection method in Non-patent document 3, while the Seebeck coefficient is actually measured, for the first time, in the range of 900K to 1600K from the Thomson coefficient for platinum metal by the current injection method in Non-patent document 4.
Moreover, non-patent documents 5 and 6 disclose a thermoelectric power measurement apparatus in which an AC method is adopted. Both relate to a method of measuring the thermoelectric power in a relative manner.